I glanced at a few of the reviews here before buying this book, and had low expectations. Perhaps that's why I enjoyed it as much as I did.
Contrary to previous comments, I thought this book provided fans of the series with some fascinating scenes regarding the making of a priestess, and Eilan's training. And latter two-thirds of the book, although not taking place in Avalon and focusing on Eilan's life in the Roman Empire, still addressed the Goddess and pagan religions and the spread of Christianity, which gave a wonderful historical perspective.
As a life-long fan of "The Mists of Avalon" and a non-Christian, I found the domination of Christianity depicted in this book to be oppressive, as did other reviewers. But it is historical, after all, and I would rather explore how such a thing came to pass and better understand it, in any case.
Let's face it, MZB fans: nothing in this series was ever going to be as great, as magical, as special as "Mists". It's a once-in-a-lifetime book, and it touched a lot of our lives. I though "The Forest House" was disappointing, and "Lady of Avalon" less so, but the comparison to "Mists" is what doomed both of them, for me at least. This book, "Priestess of Avalon", was from such a different perspective that I was less inclined to compare it to the progenitor of this series, and therefore I enjoyed it more, on the whole. Give it a chance, if you haven't read it yet, and just go in with an open mind.